Noise Performance Analysis of Differential Active Balun Transformer Circuit

A balun (balanced-unbalanced) circuit is a type of transformer that converts signals that are single-ended or unbalanced with respect to ground into signals that are differential or balanced with respect to ground, and vice versa. Fig. 1 illustrates a typical balun circuit that transforms signal from single-ended input voltage (Vin) into differential output voltages (V+ and V-) with half the amplitude of Vin and 180° phase difference. An ideal balun generates a pair of differential output signals of balanced amplitudes (0 dB gain difference) and phases (180° phase difference) from a single-ended input signal source.